Research On An Embedded Linux Filesystem Oriented To Root Filesystem

Recently, embedded Linux has been widely used in many fields, including industry control, information appliance, and individual digital terminal. The study on embedded Linux and its improvement have been one of the most popular researching fields. Root file system, as an important component of embedded Linux, was used in overall management for system resources which properties will have directly impact on system efficiency.JFFS2 is a log-structured file system designed specifically for use on Flash Memory, which source codes are open and structure is simple. JFFS2 that has functions of power-off protection and garbage collection is one of the most commonly used file system. As an universal Flash file system, JFFS2 has special advantages, but it is not ideal in security when applied in embedded Linux root file system, and it needs optimal modification.Firstly, related knowledge about embedded Linux file system and implementation mechanism of JFFS2 file system were thoroughly studied, then error-collection capability and garbage collecting strategy were probed and improved. To reinforce the security of file system, extended BCH (32, 21) codes were introduced in JFFS2 file system, while original CRC32 check which only has error-checking ability was retained. After modification, CRC32 check was conducted firstly when file system was read. If check was failed, BCH code was initiated to rectify. To overcome the low efficiency of garbage collection and uncertainty of wear control balance, erasing block structure of JFFS2 file system was improved. A counter was introduced in the last of every erasing block, recording the erasure degree of every erasing block. Before garbage collection, the erasure degree of each erasing block was checked to determine whether the difference between them has transcended the definite threshold value. If it transcended, garbage collection was performed according to balance control; if it did not, garbage collection was conducted according to collecting efficiency. The collecting efficiency of garbage collection was improved maximally under condition that assures loss balance.Finally, implementing process and properties test of file system in concrete application environment were introduced and overall paper was summed up.